This invention relates generally to hydraulic actuators and more particularly to hydraulic actuators to develop hydraulic forces for tools such as dies or dieless compressors for applying compression accessories to stranded conductors, cutting devices and the like. The hydraulic actuator of the invention utilizes a main pump and an auxiliary pump to rapidly develop a relatively large useable hydraulic force with a minimum of exertion by the operator. The main pump develops a relatively high pressure utilizing a low volume of fluid to create the primary working force, while the auxiliary pump develops a relatively low pressure with a high volume of fluid for initial rapid advancement of a working piston relative to a work piece. Both the pumps are hand operated by swinging of two handles relative to each other without changing hand positions.
Hydraulic compressing devices are known in the prior art. For example, U.S. Pat. No. 2,815,646 issued to Swanson on Dec. 10, 1957 discloses a hydraulic compression tool having a main pump which is operated by the swinging of two handles toward and away from each other for pumping fluid into the main cylinder to advance a movable die toward a fixed die to develop a compressing force. An auxiliary pump is provided in Swanson to facilitate advancement of the movable die under low pressure toward the fixed die and against the element or work piece prior to the much slower operation of the device's high pressure pump. However, in order to accomplish such advancement, devices of this type have an inherent disadvantage. An operator must continuously rotate one of the handles to operate the low pressure pump until the pre-pressing, work piece engagement of the movable die is obtained. Therefore, each time the movable die element of such device had to be advanced and/or retracted relative to a work piece through utilization of the low pressure pump, the operator had to manually rotate one of the handles with one hand in a cranking motion while gripping and supporting the device with the other hand on the other handle. Since compression tools of this type often weigh as much as twelve or more pounds and require frequent use by an operator while holding the tool above his shoulder or head level, a great deal of effort can be involved in supporting the weight of the tool with one hand by one of the handles while manually cranking the other to operate the low pressure pump prior to applying a scissors stroke to the handles to operate the high pressure pump.
Prior art devices, such as illustrated in the patent, utilized pressure relief means to relieve the substantial pressure developed during a compression operation. This enabled the operator to perform a second compressing operation provided no head adjustment was required, i.e., expansion or contraction of the die opening for various cable diameters. However, should a head adjustment be required, the operator had to resort to manual rotary cranking to effect the adjustment, a distinct disadvantage where head adjustments were required.
Another disadvantage inherent in prior art compression tools involve permanent securement of the compression head unit to the actuator body of the hydraulic device. This made interchangeability of head units for different applications impossible. Because such head units were permanently secured to the body of the actuator, the hydraulic fluid reservoir of the actuator was of a capacity sufficient only to accommodate operation of the integral head unit of the device. Therefore, use of a head unit other than that secured to the device was not intended and head units requiring greater hydraulic fluid capacities could not have been used.